1. Field of the Invention
The present invention relates to a color image display apparatus comprising a flat displaying apparatus with a number of (for example fifteen) line cathodes.
More particularly, the present invention relates to a color image display apparatus for displaying color image by means of a phosphor screen and a plural number of parallel disposed line cathodes wherein pulse width modulation is used to control electron beams.
2Description of the Prior Art
Hitherto, for an image display apparatus for a television set, a cathode-ray tube having a single electron gun, or three electron guns set in a neck part of a bulky cone shaped vacuum enclosure, has been used for long time. The shortcoming of the conventional cathode ray tube is a large depth in comparison with the size of the screen face, preventing the manufacture of a flat and compact television set. Though EL display apparatus, plasma display apparatus or liquid crystal display apparatus has been developed, these are not sufficiently usable for practical use because they have problems in brightness, contrast or color displaying.
As a novel flat type image display apparatus using electron beams, the applicant has proposed an invention in a senior Japanese Pat. Application Sho 56-20618 (published in the Japanese un-examined Pat. Application Sho 57-135590 which was published only after the priority date of the present case). This senior Japanese application serves as one priority document for Lyehara et al. U.S. Pat. No. 4,451,846. The art of the senior application is a color display apparatus comprising:
a color phosphor screen comprising a first predetermined number of horizontally divided sections each comprising a set of regions of primary color phosphors disposed in horizontal direction,
electron beam source means for in-turn emitting a second predetermined number of horizontal rows of electron beams, each row having the first predetermined number of electron beams, producing one horizontal line on the color screen,
horizontal deflection means for selective impingements of the electron beams on the regions in turn selected corresponding kinds of primary color phosphors at one time, in turn changing colors of the horizontally divided sections,
vertical deflection means for vertically deflecting the electron beams in such a manner that electron beams of a horizontal row impinges the phosphor screen in one vertically divided segment which is corresponding to the one horizontal row, thereby vertically moving the one horizontal line in the vertically divided segment,
electron beam control means for simultaneous controlling of intensities of respective electron beams responding to color video signal for the selected kind of primary color to produce a line-at-a-time displaying of color video picture, and
a flat shaped vacuum enclosure containing the above-mentioned components therein, one end face thereof forming a screen face in which the color phosphor screen is provided.
The line-at-a-time type displaying is suitable for display apparatus of the flat type CRT, liquid crystal panel, EL panel, LED panel, plasma panel or the like flat type display apparatus. Such line-at-a-time type image display apparatus generally displays an image by storing video signal information for a period of one horizontal scanning line and reading out the stored data for that one line at a time in the immediately subsequent horizontal fly-back period.
One preferred inventors' prior art apparatus is shown in FIG. 1, wherein from the back part to front part the following components are provided in a flat box-shaped enclosure.
Incorporate herein by reference the U.S. Pat. No. 4,451,846 to Iyehara et al, issued May 29, 1984, column 2, line 32 through column 8 line 35 thereof and column 8 lines 48 through 64 thereof.
However, the above-mentioned inventors' prior art apparatus has the following technical problem. A first problem is that depending on dispersions of capacitances of capacitors used as analog memory in the sample hold circuits 31.sub.1, 31.sub.2 . . . , the output levels disperse. A second problem is that the sampling clock are not necessarily stable. Unless the stability is improved by, for instance, utilizing PLL circuit, the unstability factor of the clock signal results in horizontal non-lineality of the deflection, if there is expansion and contraction of the displayed image or low color impurity due to inaccurate impingement by electron beams on partly erroneous color phosphors. However an independent stable PLL circuit is constituted, the cost of the circuit becomes very much expensive since a quartz oscillator of a very high stability is necessary as the reference oscillator. Therefore, the present invention proposes more economical and sufficiently stable circuit.